This invention relates generally to radiation imaging systems and more particularly to imaging systems having extended fields of view.
As is known in the art, radiation imaging systems have been used to diagnose tumors and other diseased tissues. Typically, small amounts of radio isotopes, after being administered to a patient, concentrate differently in the diseased and healthy tissues. The different concentrations of radiation, usually gamma rays, emitted by the healthy and diseased tissues are thus distinct and can be detected. Further, such imaging systems have been used to form images of various human organs. For cardiac imaging and dynamic function studies it is generally desirable that the camera be relatively small, relatively transportable, and have high resolution and uniformity with an adequate field of view size.
As is also known, the cameras used in providing an image of a radio active source are frequently comprised of a scintillator crystal and a collimator for guiding radiant energy from the source to the scintillator crystal. An array of photomultipliers is positioned on the opposite side of the scintillator crystal for receiving flashes of light emitted by the crystal in response to the incident radiant energy. Typically, the measure of light energy recovered by each photomultiplier is obtained by integrating circuits coupled to each of the photomultipliers, the relative magnitudes of these energies serving to indicate the location of each of the light flashes on the crystal. The signals produced by the integrators are combined in an appropriate weighting circuit to provide points on display, such as a cathode ray tube display, which correspond to the points of illumination upon the scintillated crystal. A circuit having an electronic window or gate, frequently referred to as a pulse height analyzer, is utilized in coupling the signals from the photomultipliers to the display to ensure that only signals having an energy within a prescribed range of energies are coupled to the display. Since, as noted above, for cardiac imaging and diagnostic function studies it is generally desirable that the camera be relatively small, readily transportable and have a high resolution and uniformity, it is desirable to provide a camera having a given number of photomultipliers with a maximum possible field of view.